It is known to propel a boat or other water craft using a pump jet apparatus mounted to the hull, with the powerhead being placed inside (inboard) the hull. The drive shaft of the pump jet apparatus is coupled to the output shaft of the inboard motor. The impeller is mounted on the drive shaft and housed in a jet propulsion duct or water tunnel.
To facilitate use of pump jet-propelled boats in shallow water, it is known to mount the pump jet at an elevation such that the pump jet does not project below the bottom of the boat hull. In one type of design, part of the pump jet apparatus is installed inside the hull while the remaining part penetrates the transom and extends to the rear of the hull. An inlet housing of the pump jet has a horizontal opening and an inlet ramp for guiding water into a water tunnel where the impeller resides. The horizontal opening of the inlet housing is mounted in a hole in the bottom or near the bottom of the hull.
When operating a pump jet-propelled boat in shallow water, it is possible to ingest seaweed and other debris into the housing when water is being drawn into the pump jet inlet. To prevent seaweed and other debris from entering the pump jet housing and possibly ensnarling or damaging the rotating impeller, a grate or screen is typically placed across the inlet opening. During continuous use of a pump jet-propelled watercraft in shallow, weed-infested water, floating weeds can accumulate on and become entangled with the inlet grate to such a degree that the inlet grate becomes clogged. In particular, in the case where the inlet grate comprises an array of mutually parallel tines, the suction created by the impeller causes weeds and other debris to wrap around the tines of the grate and slide rearwardly along the tines. The buildup of weeds, if allowed to continue unabated, can ultimately form a dense mass that reduces the intake of water through the inlet opening and into the pump jet. Reduced water flow can cause the jet pump to stall and the boat to stop moving.
The result is that the boat operator must unclog the inlet opening by removing the dense mass of entangled weeds from the tines of the inlet grate. However, removing entangled weeds from the inlet grate can be very difficult. This task can also be unpleasant if a person has to enter the water and submerge under the boat to remove the weeds. Moreover, even if the entangled weeds are successfully removed, when boat operation is resumed and the boat operator attempts to leave the weeded area, the inlet grate may become plugged after only a short distance, repeating the same clean-out problem.
One attempt at a solution to the problem of clogged inlet grates was disclosed in U.S. Pat. No. 5,577,941. In that disclosure, the inlet grate comprises a plurality of cantilever tines which extend rearwardly across the water intake and have suspended aft end tips spaced from the aft end of the water intake. This spacing enables rearward sliding of weeds and other debris along and then off of the cantilever tines without clogging. U.S. Pat. No. 5,577,941 characterizes this anti-clogging feature as being "automatic", with no additional mechanism being needed for unclogging.
U.S. Pat. No. 5,876,258 purports to be an improvement over the teaching of U.S. Pat. No. 5,577,941. In particular, U.S. Pat. No. 5,876,258 states that the inlet grate of U.S. Pat. No. 5,577,941 is problematic because the size of the gap between the end tips of the tines and the aft end of the weed grate plate limits the size and amount of weeds that can pass through the gap and through the pump jet. Thus, large clumps of weeds which have a thickness greater than the gap between the tines and the aft end of the inlet grate can cause clogging. Instead, U.S. Pat. No. 5,876,258 proposes an inlet grate comprising a plurality of cantilever tines each joined to a pivot rod. The cantilever tines extend across the inlet opening to prevent debris from entering the pump jet. A spring member is mounted between the cantilever tines and a mounting frame such that the spring member provides an outward rotational bias force against the rotatable cantilever tines. During operation of the watercraft, if a mass of weeds becomes clogged in the cantilever tines, the upward and inward suction force of the pump jet causes the cantilever tines to rotate upward against the opposing rotational bias force of the spring member. This self-activating mechanism allows the weeds to slide off of the ends of the cantilever tines and be ingested by the pump jet. This has the disadvantage that large volumes of weeds will plug up the pump jet at the impeller, making clean-out even more difficult than with a fixed-grate system. Also, when the inlet grate is open, hard debris, such as oysters, stones and sticks, can enter the pump jet, causing damage to the impeller.
There is a need for an inlet grate clean-out mechanism which can be actuated by a boat operator when conditions require and without ingested weeds or debris into the pump jet.